Patent GB-618952-A (GB)
Title: Apparatus for detecting the occurrence of a sequence of events
IPC: B61L1/16
Filed: 1945-11-05
Abstract: 618,952. Electrical counting apparatus. AUTOMATIC SIGNAL CORPORATION. Nov. 5, 1945, No. 29336. Convention date, Dec. 21, 1944. [Class 106 (i)] An electronic counter, broadly equivalent to the electromagnetic counter described in Specification 565,670, is applied to the counting of vehicles passing along a road and momentarily depressing three of a number of treadle plates at one time. As shown, there are four treadle plates A, B, C, D, depression of which in that order, or the reverse order, operates a forward counter FC, or a reverse counter RC, respectively. The system operates satisfactorily if any one plate jams, but if two plates jam closed, an alarm operates. A primary control triode VT3a is normally non-conducting, but when two of the plates A-D are depressed, to short-circuit two of the resistances 16-19, the grid potential is raised sufficiently for the tube to conduct, and the potential of conductor 23 therefore falls. Considering the forwardcounting circuit F only, with any three treadle plates open, tube VTla of a thermionic toggle switch VT1 is conducting and tube VT1a of a thermionic toggle switch VT1 is conducting and tube VT1b non-conducting. When two treadle plates are closed, the potential on conductor 23 and therefore on the grid of tube VTla falls, but not sufficiently to render the tube VTla non-conducting. Considering tube VT2a, when the plates A, B are open the grid potential applied via conductors 33, 34 is low, but when the plates A, B close to short-circuit resistances 16, 17 the grid potential rises and the tube VT2a conducts, its cathode potential rises and raises the grid potential of the tube VT1b which then conducts, tube VTla shutting down. Further movement of the vehicle closes plate C. Tubes VT3a and VT1b remain conducting. With tube VTla non-conducting, the lead 44 raises the plate potential of tube VT2b, the grid of which is connected to the plates A and B, so that the tube VT2b conducts while these plates are closed. When either of plates A or B is released, tube VT2b becomes non-conducting and over conductor 51 reduces the negative grid bias of a gas-filled tube VT4, which is therefore primed. This condition remains until the vehicle passes over the treadle to release plates A, B and C, whereupon the tube VT3a becomes non- conducting and applies a positive pulse over lead 23c to the grid of tube VT4 which then fires to actuate a solenoid FC to advance the ratchet of a counter one step, at the end of which a contact 62 opens and the tube VT4 extinguishes, and the system is ready for the next count. The reverse travel circuit R is identical with the forward circuit F, connections being made to D and C plates instead of A and B. Interlocks. Tubes VT2a, VT6a receive positive power from the plate circuits of VT5b, VT1b respectively. In forward travel, therefore, when plates A and B close, tube VT5b cannot be toggled to conducting condition, and when plates C and D close, although the grid of tube VT6a reaches conducting potential, the interlock with tube VT1b which continues to conduct, prevents tube VT6a from conducting. Partial operation. If a vehicle depresses plates A and B and then rolls back to release one or both, tube VT4 does not prime and no count takes place. If the vehicle depresses plates A, B and C and then releases plate C, the tube VT4 primes and then deprimes without firing. Alarm system. If two or more plates are closed for more than a certain time, an alarm actuates. Tube VT3b is normally conducting. As soon as two or more plates are closed, tube VT3a conducts and via leads 23, 92 lowers the grid potential of tube VT3b which shuts off after a time determined by the condenser 96. Contacts 95 then close to operate a lamp L, a printer PRT or a bell BL. The four-treadle system can be replaced by three, the middle plate performing the functions of plates B and C. In this case, the system fails if one plate jams.